الفهرس 
Physics Of The PentacamOnly 14 pages are availabe for public view
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Abstract
The Pentacam represents a significant advancement in corneal and anterior segment imaging. The Pentacam utilizes two cameras. The central one is used for fixation monitoring and pupil measurement. While the second is rotating Scheimpflug imaging camera. (Belin and Khachikian, 2007)
●The Scheimpflug principle was developed by Theodor Scheimpflug of Austria. It employs a slanted setup of subject, lens and film plane. This setup allows for extended depth of Field. Since the Scheimpflug camera rotates around the corneal center central resolution is high. This is in stark contrast to Placido-based measurement which lack central data due to the position of camera. (Maus and Krober, 2007)
●A typical measurement provides 25 or 50 3D images in different planes during a scan of less than two seconds duration. Each image typically contains approximately 500 true elevation points which are then analyzed to yield 12,000 – 25,000 total data points. (Belin and Khachikian, 2007)
●The oculus pentacam is a multipurpose instrument that is capable of external ocular photography, corneal pachymetry, corneal topography, densitometry and anterior chamber analysis. The oculus pentacam provides the user with the ability to view, photograph and measure the anterior segment of the eye without invasive operation or direct contact with the eye. (Aristides al., 2007)
●Pentacam topography is better than convential topographer because the former is elevation based & not Placido disc based with showing an anterior & posterior elevation map in addition to curvature map to better analysis of the cornea. (Aristides al., 2007)
●For calculating corneal thickness, the camera measures from the top of the epithelium to the anterior surface of the endothelium. Importantly, it does not measure the tear film. The corneal thickness is displayed as a color image and can be evaluated at any particular location by clicking on the area or by using the numerical function. (Grewal, 2008)
●The Pentacam features automatic Keratoconus detection. Progression of keratoconus and following treatment with newer technologies like corneal collagen crosslinking and Intacs¨ can be monitored. (Maus and Krober, 2007)
●The Belin/Ambrósio Enhanced Ectasia Display of the Oculus Pentacam, combine anterior and posterior elevation and pachymetric data for a complete overview of the corneal structure. The combination of the pachymetric graphs and indices and elevation maps, which utilize an enhanced reference sphere, enables an increased sensitivity and specificity in the screening of patients for ectatic disease. (Belin and Khachikian, 2009)
●The Pentacam can generate the wavefront map of the cornea. The anterior and posterior corneal surface is described separately by Zernike polynomials based on the measured elevation data that allows the ophthalmologist to make better decisions regarding the IOL design & also in wavefront customized LASIK. (Oculus, 2008)
●In the “Holladay Report” incorporated in the Pentacam software the ratio between back and front power of the cornea is calculated for the current examination as well as the “Equivalent K-Readings” of the cornea. (Grewal, 2008)
●The Pentacam provides a comprehensive, precise and valid measurement of corneal power and optical aberrations that allows the ophthalmologist to make better decisions regarding the IOL design and power, particularly in cases with abnormal corneas, either from ecstatic conditions or previous keratorefractive surgery. The measurement obtained from the Pentacam in abnormal corneas should be used in combination with formulas designed for this particular instrument. (Viteri, 2008)
● The Pentacam Tomography calculates a virtual model of the anterior segment of the eye including the cornea. It is possible to move, zoom and rotate it to detect the depth and the size of any opacity in the cornea. (Oculus, 2006)
●The Pentacam is useful in managing post-PKP patients especially in decision making with respect to suture removal. Another interesting application is in diagnosing Capsular Bag Distension Syndrome. Also the Pentacam identify subtle corneal opacities and follow the changes over time such as in adenoviral keratoconjunctivits. (Grewal, 2008)
●The Pentacam illustrates the location of implantable phakic IOL’s positioning in relation to crystalline lens as well as cornea, AC angle during the pre-op assessment. This allows the ophthalmologist to follow up these patients with ICL for monitoring their risk for developing cataract. (Grewal, 2008)
●For glaucoma screening, Anterior Chamber Volume has been found to be a good screening tool for diagnosing eyes with narrow angles. The software provides a colored map of the anterior chamber depth-both central and peripheral. Also the software allows for IOP modification taking into consideration the corneal thickness. (Grewal, 2008)
●However it is limited in its evaluation of the anterior chamber angle. Direct angle visualization of the scleral spur, ciliary body, and ciliary sulcus is possible only with the Anterior Segment OCT and UBM; not the Pentacam. (Grewal, 2008)
●Opacification of the crystalline lens can be quantitatively imaged and analyzed using the Pentacam. The grading of lens density through Scheimpflug images has been found to correlate well with the LOCS III grading system for cataracts. This densitometry helps in choosing the power modality during pacoemulsification.It is also excellent tool for identifying intralenticular foreign bodies. (Grewal, 2008)